Semiconductor devices are widely used in an electronic industry because of their small size, multi-function, and/or low fabrication costs. High-performance and low-cost semiconductor devices have been increasingly demanded with the development of the electronic industry. Semiconductor devices (e.g., semiconductor memory devices) have been highly integrated in order to satisfy the above demands.
An integration degree of a conventional two-dimensional (2D) memory device is mainly determined by an area occupied by a unit memory cell. Therefore, the integration degree of the conventional 2D memory device is greatly affected by a technique for forming fine patterns. However, there may be some limitations in increasing the integration degree of the semiconductor memory devices due to high costs of apparatuses used in fabrication of the semiconductor memory devices and/or difficulties of fabrication processes. Three-dimensional (3D) semiconductor devices including three-dimensionally arranged memory cells have been developed to overcome the above limitations.